Study finds olfactory impairment to increase the risk of cognitive decline
A new study published in the journal of International Forum of Allergy and Rhinology showed that the individuals with olfactory impairment (OI) had double the prevalence of cognitive decline (CD) when compared to people with normal olfactory perception.
Due to the fact that OI is a common symptom of COVID-19 and that many patients have ongoing symptoms, this previously disregarded sensory impairment has gained attention. Dementia and cognitive impairment are both crippling illnesses that can lower a patient's and family's quality of life and increase both individual and national healthcare costs. Thus, this study aimed to summarize the long-term relationship between OI and CD by synthesizing the existing evidence in a systematic review and meta-analysis.
Through August 9, 2024, Web of Science and Embase PubMed were searched for longitudinal studies that reported on self-reported and objectively evaluated OI in relation to CD using validated methodologies. Incident CD was the result of interest. Data extraction, bias assessment, and evidence strength grading were done by independent writers. Subgroup, sensitivity, and bias analyses were performed as part of a mixed-effects meta-analysis. OI-associated CD's population-attributable fraction (PAF) was computed.
There were 37,783 participants and 48 papers in this research. When compared to people with normal olfaction, OI patients had a 2.06-fold higher risk of any CD (risk ratio [RR] = 2.06; 95% CI = 1.87‒2.26, I2 = 0%). In comparison to individuals with mild OI (RR = 1.51; 95% CI = 1.23‒1.85, I2 = 0%), those with severe OI had a greater risk of any CD (RR = 2.60; 95% CI = 2.12‒3.20, I2 = 0%).
Every 10% drop in olfactory score (RR = 1.18; 95% CI = 1.14‒1.22, I2 = 24%) and every point drop on the Sniffin' Sticks Odor Identification Test (RR = 1.15; 95% CI = 1.11‒1.18, I2 = 0%) raised the probability of any CD by 18%. These findings held up well to additional examinations. The PAF of incident CDs linked to OI was 18%.
Overall, OI with higher category severity and deteriorating olfactory scores was linked to a higher risk of CD, according to a positive categorical and continuous dose-response association. Cognitive screening should be advised for individuals with chronic OI, and OI may be included as a component of early cognitive screening in high-risk patients.
Source:
Yeo, B. S. Y., Song, H. J. J. M. D., Tan, B. K. J., Suresh, A., Ho, O. T. W., Chan, J. H., Gao, E. Y., Tan, C. J.-W., Teo, C. B., Chen, C. L.-H., Tay, L., Lamoureux, E. L., Hummel, T., See, A., Xu, S., Toh, S. T., Charn, T. C., & Teo, N. W. Y. (2025). Olfactory impairment and incident cognitive decline: A systematic review and meta-analysis. International Forum of Allergy & Rhinology, e23635, e23635. https://doi.org/10.1002/alr.23635
